Electric heater



Feb. 3, 1942. E. s. SMITH ELECTRIC HEATER Filed May 23, 1938 2 Shets-Sheet l INVENTEIR (295.91%.

is formed;

?atented Feb. 3', 1942 amc'mrc HEATER OFFICE Elmore Stanley Smith, Weston, Ontario, Canada, assignor to Mofiats Limited, Weston, Ontario,

Canada Application May 23, 1938, Serial No. 209,438 incanada June 30, 1937 2 Claims.

lhis invention relates to electric heaters and particularly to those of the sheathed element type having a casing or sheath formed of sheet metal for enveloping a resistor and my object is to provide a heater of this type which is simple, strong, durable and easily made and which will form a good heat conducting path between the resistor and a cooking vessel placed on the heater whereby quick heating effects are obtained.

A further object is to so construct the sheath that it may be conveniently formed into a grid, the parts or combinations of which are readily anchored to suitable supporting means to hold said parts in suitable spaced relationship and with their upper surfaces in substantially the same plane.

I attain my object by means of constructions which may be briefly described as follows. The sheath is formed from a flat bottomed channel shaped strip of sheet metal, the channel having its margins directed laterally from the sides thereof. After the channel has been. filled with insulating material and a resistor, a hat strip of metal preferably is inserted and the upper parts of the sides of the channel are turned inwardly to close the initially opened top of the channel. The said margins are thus brought into close re lationship and project outwardly from the sheath so that they may be conveniently welded or otherwise secured together to seal the sheath and form a continuous rib or flange. The element may be bent to form a grid having the fiat underside of the sheath uppermost and the flange depending from the sheath. The grid is anchored by any suitable means connecting together different portions of the flange to hold parts of the grid in spaced relationship to one another and to prevent the grid from twisting. Preferably, parts of the flange are passed through openings in a channel member beneath the grid, and the lower ends of the said flange parts are deformed to secure them to the channel member.

The constructions are hereinafter more fully describedand are illustrated in the accompanying drawings, in which Fig. 1 is a perspective view of a strip of sheet metal, partly broken away, from which the sheath Fig. 2 a cross section of the sheath strip material formed into a channel having its margins laterally directed;

Fig. 3 a view similar to Fig. 2 showing insulating powder inserted in the bottom of the channel;

Fig. 4 a view similar to Figures 2 and 3 showing the resistor inserted;

Fig. 5 a view similar to Figures 2, 3 and 4 showing more insulation and a narrow strip of metal inserted in the channel;

Fig. 6 a, cross-sectional view showing diagrammatically how the upper parts or the sides are bent in over the edges of the narrow strip while the latter is held in position;

Fig. 7 a cross-sectional view showing the sheath completely closed;

Fig. 8 a plan view of a. heater employing two of the sheathed elements;

Fig. 9 a cross-section on the lines 9-9 in Figure 8;

Fig. 10 a cross-section on the lines iii-id in Fig. 8;

Fig. 11 a front elevation'of the heater; and

Fig. 12 a perspective detail of the channel memher to which the heater anchoring convolutions are secured.

In the drawings like numerals of reference indicate corresponding parts in the dififerent figures.

Referring to Figures 1 to '7, the heating element comprises a sheath formed or a strip of sheet metal which is first formed into a channel 5 having its margins 2 directed laterally from the sides 3. insulating powder 6 having good heat conducting properties is deposited in the flat bottom i of the channel and pressure is applied to compact it therein and shape it to receive a resistor 5. The latter may be a helical coil of resistance wire flattened out by passing it between rollers.

Each end of the resistor 5 is provided with a terminal or lead-in 6 which may be welded or otherwise secured to the end of the wire 5. The terminals 6 extend beyond the ends or the channel and are insulated therefrom by any suitable means such as a plurality of layers of mica or a block 5 of other insulating material. The layers or blocks are adapted to be tightly received in the ends of the channel, to prevent the. escape of powder therethrough, and preferably extend slightly beyond the ends of the channel, More insulating powder 4 is then deposited in the channel to cover the resistor and this powder is compressed to compact the powder around the resistor. the insulating material 4 which is below the upper parts 3 of the sides of the channel. The said upper parts 3 are then bent in by any suitable means while a tongue 9 holds the strip 8 inplace to prevent the insulating material from' escaping. When the bent-in parts 3 engage the edges of the strip 8, the tongue 9, which extends A strip of metal 8 is placed on top 0! the full length of the strip, is withdrawn. The upper parts 3 are then again forced inwardly by any suitable means to their flnal position in which they overlie the strip 8.- The channel is thus closed throughout its length and the terminal insulations 6' are also covered. Referring to Fig. '1, it will be noted that the margins 2 now project outwardly from the body of the channel in close relationship to one another. The next step is to electrically weld these margins to seal the channel and this may be accomplished by a series of closely spaced spot welds or by a continuous weld produced by passing the margins 2 between two rollers in a resistance welding machine. The margins when welded together form a rib or flange 2* which extends the full length of the channel for purposes which will be described later.

Preferably the lnsulatingpowderisslightlymoist when it is inserted in the channel in which case the channel is placed in a drying oven to remove all traces of moisture from the compressed powder and the interior of the channel before the latter is sealed. In practice, the powder is compressed under a pressure of from 2 to 12 tons per square inch. As a result of this high pressure, the powder becomes a mass of compacted material which forms a good conductor of heat and also a good electrical insulator.

The sheet metal of which the channel or sheath l is formed is an alloy of suitable metals adapted to withstand high temperatures for a long period of time. Thls alloy is well known in the art and the heating element comprising the sheath I, the compacted powder 4, I and the resistor 5 may be bent or curved to any desired shape of grid. After the element is bent it will be necessary to use the underside I of the channel as the top of the element, in which case the flange 2 will extend downwardly from the underside of the element. Th flat top l provides a maximum contacting surface, extending from side to side of the sheath, for-engagement with the bottom of a cooking vessel.

In Figures 8 to 11, is shown a heater of the hot plate type comprising two sheathed heating elements I", I each of which formed of a predetermined length of channel and subsequently bent or curved so that it will co-operate with the other element to form a grid id. The ends of the elements are passed through openings in the top of a terminal box II and secured therein in any suitable manner to form grease-proof joints betwen the edges of the openings and the ends of the elements. The box II is provided with upwardly extending lugs I! which are pivoted at I! on any suitable stationary part l3 of a stove so that the heating grid may be swung upwardly relative to the cooking top 20 of the stove.

The convolutions of the grid are secured together and the grid is supported as follows: A channel member ll extending across the underside of the convolutions oi the grid I is provided with spaced apart openings ii for receiving the portions of the flanges 2' overlying the member ll. The depth of the flanges 2* is greater than the thickness of the material of which the channel member i4 is formed so that portions oi the flanges will. extend through the openings l into the groove of the channel member. The protruding portions are burred or deformed to secure the flanges in the openings. When the grid is spiral the channel member M will extend diametrically across it and be arranged substantially parallel to the axis of the pivotal connection for the terminal box II. A second channel member ID extends substantially at right angles to the member ll across the underside of the portion of the grid remote from the pivotal connection I3. The member ll is also provided with spaced apart openings II for receiving the portions of the flanges 2' overlying the member it. The inner ends of the portions of the flanges received in the openings in the member It are also deformed to secure the flanges thereto. with this construction the convolutions of the grid are flrmly secured in spaced relationship to one another and yet they are free to expand and contract between the points of connection with th members ll, I8 and the box H.

The channel members II and it rest on a reflector ll which is removably carried on a plurality of adjustable supports i8 which may be set screws threaded in lugs I9 formed on or secured to the underside of the cooking top II. The lugs project inwardly from the wall of the usual opening in the cooking top to receive the hot plate and are so located relative to the upper surface of the cooking top 20 that the top of the grid will be positioned slightly above the upper surface of thecooking top. The reflector is provided with a rim which extends upwardly around the outer convolutions of the grid II to a point adjacent the underside of a vessel resting on the grid. The rim and the bottom of the reflector are cut away at 22 to clear the ends of the sheathed elements which pass downwardly from the convolutions to the terminal box il located below the reflector.

By swinging the grid on its pivots l3 to raise it clear of the reflector, the latter may be readily removed from its supports l8 for cleaning and polishing purposes. The terminals or lead-ins l are flexible, are insulated from one another and from the terminal box II in any suitable mannet, and are directed through insulated openings 23 therein to stationary contacts or direct to a switch (not shown).

The spiral grid type of hot plate enables a considerable length of heating element or elements to be confined in a relatively small area such as would be covered by ordinary cooking vessels. To obtain the best heating results it is not only necessary that the top surfaces i of the elements be flat to provide the maximum width of contact area (relative to the width of each element) between the elements and a vessel supported thereon but that the flat top surfaces i be flush so that the maximum contact area throughout the total length of the convolutions will be obtained. After each element is curved or bent to the de-- sired shape, it is subjected to a high pressure to ensure that the tops l of the convolutions are level. The rigidity of the continuous ribs or flanges 2' on the undersides of the elements tends to retain the convolutions as set because the flanges resist any bending of the convolutions in a vertical direction.

The convolutions are firmly held from shifting or twisting relative to one another by the channel members l4, it which are anchored firmly to the flanges 2'.

It is obvious that various modifications of my invention may be made without departing from the spirit of the invention as defined by the accompanying claims.

what I claim as my invention is:

1. A method of forming a sheathed electrical heating element which consists in forming a U- shaped channel of an integral sheet of metal with substantially parallel side walls having their margins extending outwardly from said side walls and away from one another; inserting a resistance wire in said channel and embedding it in insulating material, the said material extending only part way up the side walls of the channel; bending in the upper parts of the side walls of the channel towards one another to close the channel over said insulating material and bring the aforesaid margins into parallel engaging relationship extending substantially at right angles to said bent-in upper parts of the side walls; supporting the inner sides of the lower side walls to hold the same in position duringthe bending in of the upper side walls; and welding said margins together to form an upstanding rib intermediate of the side walls.

2. The method of producing an electrical heating element which comprises the steps of introducing into a comparatively deep sheet metal casing having substantially parallel side walls through an open side of said casing a limited quantity of granular refractory insulating material and a resistor, the margins of the side walls being directed outwardly from the open side thereof above the insulating material and away from one another, turning in the portions of the side walls above the insulating material to overliev the latter and bring the margins into parallel engaging relationship extending substantially at right angles to the body of the sheath, and welding the margins together to form an outwardly directed rib extending longitudinally of the casing.

ELMORE STANLEY SMITH.

CERTIFICATE OF CORRECTION. Petent-No. 2,272,156. I February 5, 191 2. ELMORE STANLEY SMITH.

It is hereby certified. that error appears in the printed specification of the Above umbered pe.tent requiring correction as follows; Page 1, first column, line 12, for "combination s" read --oonvo1utions-; and that the said Lettere Patent should be readvwith this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 17th day' of March, A. D. 19h2.

Henry Van Arsdale,

(Seal) Acting Commissioner of Patents.

. v CERTIFICATE 0F CORRECTION. PetentNo. 2,272,156. 4 February 5, 19!;2. *ELMORE STANLEY SMITH.

It is hereby certified that error appears in the printed specification of theebove numbered 'patent requiring correction as follows: Page 1, first column, line 12, for "combinations" read --convo1utions--; and that the said Letters Patent should. be readwith this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 17th day of March, A. D. 1911.2.

- Henry Van Arsdale, ($851) I Acting Commissioner of Patents. 

